Technical Field
[0001] The present invention relates to galvanized steel sheets that exhibit a low sliding
friction during press forming and have excellent press-formability.
Background Art
[0002] Galvanized steel sheets are used in various fields and are frequently used for automobile
bodies. For galvanized steel sheets to be used in such an application, they are subjected
to press forming. However, galvanized steel sheets are poor in press-formability compared
to cold rolled steel sheets. This drawback arises from the fact that surface-treated
steel sheets exhibit a higher sliding friction with respect to a press mold compared
to cold rolled steel sheets.
[0003] That is, a high sliding friction is generated between a mold and a bead so as to
prevent the surface-treated steel sheet from being slid smoothly into the press mold,
often resulting in a fracture of the steel sheet. In particular, galvanized steel
sheets coated with pure zinc exhibit a higher sliding friction due to the zinc coating
having become attached to a mold (a phenomenon known as galling). As a result, cracks
are generated in the middle of continuous press forming, thus severely adversely affecting
the productivity of automobiles. Further, the recent tight restrictions on CO
2 emissions have led to a trend in which the use rate of high-strength steel sheets
has been increased for the purpose of automobile body weight reduction. When high-strength
steel sheets are used, an increased contact pressure is encountered during press-forming
and the attachment of a coating to a mold becomes a more serious problem.
[0004] A widely used method of improving press-formability of galvanized steel sheets is
to apply a lubricant oil having a high viscosity. Because of the high viscosity of
such a lubricant oil, however, paint defects occur during a painting step due to insufficient
degreasing. Further, other problems are encountered such as a destabilized press performance
caused by a lubricant being exhausted during pressing. Thus, there has been a strong
demand for galvanized steel sheets themselves to be improved in terms of press-formability.
[0005] To solve these problems, Patent Literature 1 and Patent Literature 2 disclose techniques
in which the surface of a galvanized steel sheet is subjected to an electrolytic treatment,
a dip treatment, a coating oxidation treatment or a heat treatment so as to form a
zinc-based oxide film, thereby improving weldability and processability.
[0006] Patent Literature 3 discloses a technique in which a galvanized steel sheet is dipped
into an aqueous solution containing sodium phosphate at 5 to 60 g/L and having a pH
of 2 to 6,
or is subjected to an electrolytic treatment or is coated with the above aqueous solution
so as to form an oxide film based on phosphorus oxide on the surface of the galvanized
steel sheet, thereby improving press-formability and chemical conversion treatment
properties.
[0007] Patent Literature 4 discloses a technique in which the surface of a galvanized steel
sheet is subjected to an electrolytic treatment, a dip treatment, a coating oxidation
treatment or a heat treatment so as to form nickel oxide, thereby improving press-formability
and chemical conversion treatment properties.
Citation List
Patent Literature
[0008]
PTL 1: Japanese Unexamined Patent Application Publication No. 53-60332
PTL 2: Japanese Unexamined Patent Application Publication No. 2-190483
PTL 3: Japanese Unexamined Patent Application Publication No. 4-88196
PTL 4: Japanese Unexamined Patent Application Publication No. 3-191093
Summary of Invention
Technical Problem
[0009] The above conventional techniques are effective with respect to galvanized steel
sheets with relatively low strength which are frequently used for automotive exterior
panels. However, galvanized steel sheets with high strength which undergo an increased
contact pressure during press forming cannot be necessarily improved in terms of press-formability.
[0010] The present invention is aimed at solving the problems described hereinabove. It
is therefore an object of the invention to provide galvanized steel sheets that exhibit
excellent press-formability even when the galvanized steel sheets are hardly formable
materials such as high-strength galvanized steel sheets exerting an increased contact
pressure during press forming.
Solution to Problem
[0011] Conventional films achieve a decrease in frictional resistance by intermediating
between the zinc coating and a mold. However, an increased amount of film is worn
away under high contact pressure conditions which are encountered in the press forming
of high-strength steel sheets. Thus, sufficient effects cannot be obtained after the
slide distance has exceeded a certain level.
The present inventors carried out studies in order to solve the above problem. They
have then found that a film of a crystalline layered substance which is formed so
as to coat the surface of a galvanized steel sheet is effective for markedly improving
sliding properties.
[0012] The present invention has been made on the basis of the above finding. The invention
is summarized below.
[1] A galvanized steel sheet which has an organic inorganic complex coating containing
an organic resin and a crystalline layered substance on the surface, the organic inorganic
complex coating having an average film thickness of 0.10 to 2.0 µm and containing
the crystalline layered substance in a solid content of not less than 0.5 parts by
weight with respect to 100 parts by weight of the solid content of the organic resin.
[2] The galvanized steel sheet described in [1], wherein the crystalline layered substance
is a layered double hydroxide represented by [M2+1-XM3+X(OH)2] [An-]x/n·zH2O wherein M2+ is one, or two or more selected from Mg2+, Ca2+, Fe2+, Ni2+, Zn2+, Pb2+ and Sn2+, M3+ is one, or two or more selected from Al3+, Fe3+, Cr3+, 3/4Zr4+ and Mo3+, and An- is one, or two or more selected from OH-, F-, CO32-, Cl-, Br-, (C2O4)2-, I-, (NO3)-, (SO4)2-, (BrO3)-, (IO3)-, (V10O28)6-, (Si2O5)2-, (ClO4)-, (CH3COO)-, [C6H4(CO2)2]2-, (C6H5COO)-, [C8H16(CO2)2]2-, n(C8H17SO4)-, n(C12H25SO4)-, n(C18H37SO4)- and SiO44-.
[3] The galvanized steel sheet described in [1], wherein the crystalline layered substance
is a layered double hydroxide represented by [M2+1-XM3+X(OH)2] [An-]X/n · zH2O wherein M2+ is one, or two or more selected from Mg2+, Ca2+, Fe2+ , Ni2+ and Zn2+, M3+ is one, or two or more selected from Al3+, Fe3+ and Cr3+, and An- is one, or two or more selected from OH-, CO32-, Cl- and (SO4)2-.
[4] The galvanized steel sheet described in any of [1] to [3], wherein the organic
resin is one, or two or more selected from epoxy resins, modified epoxy resins, polyhydroxy
polyether resins, polyalkylene glycol-modified epoxy resins, urethane-modified epoxy
resins, resins obtained by further modifying these resins, polyester resins, urethane
resins, silicon resins and acrylic resins.
In the invention, the term "galvanized steel sheet" is used as a collective term for
steel sheets which have been coated with zinc by any of various processes such as
hot dip coating, electrolytic coating, deposition coating and spray coating. The term
"galvanized steel sheet" includes hot dip galvanized steel sheets which have not been
subjected to any alloying treatment as well as galvannealed steel sheets which have
been subjected to an alloying treatment. Advantageous Effects of Invention
[0013] According to the present invention, a galvanized steel sheet is obtained which exhibits
a low sliding friction at a portion of the steel sheet that is at risk of being fractured
during press forming, even in the case where such a portion undergoes a high contact
pressure during press forming, and which shows excellent press-formability even at
a portion of the steel sheet that undergoes a high contact pressure and is expected
to cause the attachment of coating onto a mold.
Brief Description of Drawings
[0014]
[Fig. 1] Fig. 1 is a schematic front view of a dynamic friction coefficient measuring
apparatus.
[Fig. 2] Fig. 2 is a schematic perspective view illustrating a shape and a size of
the bead in Fig. 1 (bead shape 1).
[Fig. 3] Fig. 3 is a schematic perspective view illustrating a shape and a size of
the bead in Fig. 1 (bead shape 2).
Description of Embodiments
[0015] Conventional films achieve a decrease in frictional resistance by intermediating
between a zinc coating and a mold. However, an increased amount of film is worn away
under contact pressure conditions which are encountered in the press forming of high-strength
steel sheets. Thus, sufficient effects cannot be obtained after the slide distance
has exceeded a certain level.
[0016] The present inventors carried out studies in view of the above fact. The present
inventors have found that sliding properties are markedly improved by coating the
surface of a galvanized steel sheet with a crystalline layered substance. Further,
it has been found that a crystalline layered substance can adhere to the surface firmly
by being formed into a complex together with an organic resin. Thus, according to
the present invention, the surface of a galvanized steel sheet has an organic inorganic
complex coating containing an organic resin and a crystalline layered substance.
[0017] The mechanism by which the crystalline layered substance contained in the organic
inorganic complex coating produces lubricating effects is not clear but can be explained
as follows. During sliding, the adhesive force acting between a mold and a coating
generates a shear stress on the surface of the coating. The crystalline layered substance
intermediating between the coating and the mold is slip-deformed so as to absorb the
shearing deforming stress generated on the surface. Even after the crystalline layered
substance has been worn away from the surface layer of the galvanized steel sheet,
it becomes attached to the mold and effectively works so as to reduce the frictional
resistance. Thus, sufficient effects can be obtained even under high contact pressure
conditions simulating the press forming of high-strength steel sheets.
Further, the configuration in which the organic inorganic complex coating contains
an organic resin allows the crystalline layered substance to cover the surface of
the steel sheet in a uniform thickness.
For the reasons described hereinabove, the galvanized steel sheet according to the
invention has an organic inorganic complex coating which contains an organic resin
and a crystalline layered substance on the surface of the steel sheet. This configuration
is the most important requirement in the present invention.
[0018] The organic inorganic complex coating which contains an organic resin and a crystalline
layered substance (hereinafter, sometimes simply referred to as organic inorganic
complex coating) has an average film thickness of 0.10 µm to 2.0 µm as measured from
a cross section obtained by SEM. If the average film thickness is less than 0.10 µm,
it is difficult to form such a coating on the surface of a steel sheet uniformly.
If the average film thickness is in excess of 2.0 µm, there is a risk that spot weldability
which is an important property for the production of automobiles may be lowered.
[0019] The thickness of the organic inorganic complex coating may be measured from a result
obtained by ultralow-accelerating-voltage SEM with respect to an FIB-processed cross
section. The identification of crystal structure for determining whether the crystalline
layered substance is crystalline may be performed by thin-film X-ray diffractometry.
[0020] The crystalline layered substance is contained in a solid content of not less than
0.5 parts by weight with respect to 100 parts by weight of the solid content of the
organic resin. Any content that is less than 0.5 parts by weight is not sufficiently
high for the crystalline layered substance to exhibit desirable effects when in contact
with a mold during sliding.
[0021] In the invention, the term "crystalline layered substance" means a crystal in which
unit crystal lattices formed of plate-shaped covalent crystals are stacked on top
of one another with a relatively weak bond such as intermolecular force, hydrogen
bond or electrostatic energy. Among such substances, a layered double hydroxide that
has a structure represented by [M
2+1-X(OH)
2][A
n-]
x/n · zH
2O is a preferred crystalline layered substance because negatively charged anions bond
to plate-shaped, positively charged divalent and trivalent metal hydroxides through
electrostatic energy in order to neutralize electrical charge while these ions are
stacked on top of one another so as to form a layered crystalline structure.
Such a layered double hydroxide represented by [M
2+1-XM
3+X(OH)
2][A
n-]
x/n · zH
2O may be identified by X-ray diffractometry. It is known that a substance which can
be represented by the above formula is a layered crystal.
[0022] M
2+ is preferably one, or two or more selected from Mg
2+, Ca
2+, Fe
2+, Ni
2+, Zn
2+, Pb
2+ and Sn
2+. In particular, Mg
2+, Ca
2+, Fe
2+, Ni
2+ and Zn
2+ have been confirmed to occur naturally or synthetically in layered double hydroxides,
and are more preferable because such layered double hydroxide species give stable
layered double hydroxides.
[0023] M
3+ is preferably one, or two or more selected from Al
3+, Fe
3+, Cr
3+, 3/4Zr
4+ and Mo
3+. In particular, Al
3+, Fe
3+ and Cr
3+ have been confirmed to occur naturally or synthetically in layered double hydroxides,
and are more preferable because such layered double hydroxide species give stable
layered double hydroxides.
[0024] A
n- is preferably one, or two or more selected from OH
-, F
-, CO
32-, Cl
-, Br
-, (C
2O
4)
2-, I
-, (NO
3)
-, (SO
4)
2-, (BrO
3)
-, (IO
3)
-, (V
10O
28)
6-, (Si
2O
5)
2-, (ClO
4)
-, (CH
3COO)
-, [C
6H
4(CO
2)
2]
2-, (C
6H
5COO)
-, [C
8H
16(CO
2)
2]
2-, n(C
8H17SO
4)
-, n(C
12H
25SO
4)
-, n(C
18H
37SO
4)
- and SiO
44-. These anions have been confirmed to form layered double hydroxides by being incorporated
between layers of layered double hydroxide species. In particular, OH
-, CO
32-, Cl
- and (SO
4)
2- may be used as interlayer anions more suitably because they can be incorporated between
layers of layered double hydroxide species more easily compared to other kinds of
anions and thus films can be formed on the surface of galvanized steel sheets in a
short time.
[0025] Next, there will be described a method for forming the organic inorganic complex
coating on the surface of a galvanized steel sheet.
[0026] First, a method of forming the crystalline layered substance is described. Here,
an exemplary method is illustrated in which a layered double hydroxide that is one
kind of crystalline layered substance is prepared in the form of powder. For example,
such a double hydroxide is formed by dropping an anion-containing solution into a
cation-containing aqueous solution. An aqueous solution containing one or more kinds
of inorganic anions or organic anions (A
n-) is dropped into an aqueous solution containing one or more kinds of divalent cations
(M
2+) and one or more kinds of trivalent cations (M
3+). In this process, the pH of the reaction suspension liquid is adjusted to be 10±0.1
by dropping a 2.0 M NaOH solution.
[0027] In the reaction suspension liquid, the divalent cations and the trivalent cations
form hydroxides and are present in the form of colloids. These hydroxides are precipitated
as layered double hydroxides when one or more specific anions selected from OH
-, F
-, CO
32-, Cl
-, Br
-, (C
2O
4)
2-, I
-, (NO
3)
-, (SO
4)
2-, (BrO
3)
-, (IO
3)
-, (V
10O
28)
6-, (Si
2O
8)
2-, (ClO
4)
-, (CH
3COO)
-, [C
6H
4(CO
2)]
2-, (C
6H
5COO)
-, [C
8H
16(CO
2)
2]
2-, n(C
8H
17SO
4)
-, n(C
12H
25SO
4)
-, n(C
18H
37SO
4)
- and SiO
44- are dropped into the liquid. Next, the precipitate is separated using a centrifugal
separation apparatus and dried to give a powdery layered double hydroxide.
The obtained powdery substance may be identified as being a layered compound by X-ray
diffractometry.
[0028] Next, the obtained powdery layered double hydroxide and an organic resin are appropriately
mixed with each other and stirred to give a coating composition. The stirring may
be carried out using, for example, a coating disperser (a sand grinder). The stirring
time may be selected appropriately. The stirring time is preferably 30 minutes or
more in order to make sure that the powdery layered double hydroxide is sufficiently
dispersed in the organic solvent.
[0029] In the invention, one, or two or more kinds of organic resins may be appropriately
selected from epoxy resins, modified epoxy resins, polyhydroxy polyether resins, polyalkylene
glycol-modified epoxy resins, urethane-modified epoxy resins, resins obtained by further
modifying these resins, polyester resins, urethane resins, silicon resins and acrylic
resins. In particular, a preferred resin from the viewpoint of corrosion resistance
is an epoxy-based resin whose molecular weight has been optimized in order to achieve
improved processability or which has been partially modified with a urethane, a polyester
or an amine.
[0030] Further, one, or two or more kinds of additives may be added as required, with examples
including organic color pigments (such as condensed polycyclic organic pigments and
phthalocyanine organic pigments), color dyes (such as watersoluble azo metal dyes),
inorganic pigments (such as titanium oxide), conductive pigments (for example, powders
of metals such as zinc, aluminum and nickel, as well as iron phosphide and antimony-doped
tin oxide), coupling agents (such as titanium coupling agents) and melamine-cyanuric
acid adducts.
[0031] Next, the coating composition is applied to the surface of a steel sheet and is baked.
The coating composition may be applied to the surface of a steel sheet by any means
without limitation. A roll coater is suitably used.
The thermal drying (baking) treatment may be carried out using a dryer, a hot air
furnace, a high frequency induction heating furnace, an infrared furnace or the like.
From the viewpoint of corrosion resistance, a high frequency induction heating furnace
is particularly preferable. The thermal treatment is desirably carried out at a reached
sheet temperature in the range of 50 to 350°C, and preferably 80°C to 250°C. If the
heating temperature is below 50°C, a large amount of solvent remains in the film,
thus resulting in insufficient corrosion resistance. Heating at a temperature exceeding
350°C is not economical and can cause defects in the film, possibly resulting in a
decrease in corrosion resistance.
By the method described hereinabove, a galvanized steel sheet may be obtained which
has the organic inorganic complex coating containing the organic resin and the crystalline
layered substance on the surface.
[0032] In the production of hot dip galvanized steel sheets or galvannealed steel sheets
used in the invention, it is necessary that Al be added to the plating bath. However,
elements other than Al which may be added are not particularly limited. That is, the
advantageous effects of the invention are not deteriorated even when the plating bath
or the coating contains Al and other elements such as Pb, Sb, Si, Sn, Mg, Mn, Ni,
Ti and Li.
[0033] Further, the advantageous effects of the invention are not deteriorated even when
elements such as N, Pb, Na, Mn, Ba, Sr and Si are incorporated into the organic inorganic
complex coating as a result of the contamination of treatment liquids used for the
film production with such impurities.
EXAMPLES
[0034] The present invention will be described in greater detail by presenting examples
below.
Layered double hydroxides were prepared by dropping an aqueous solution containing
at least one kind of inorganic anion or organic anion (A
n-) (Composition of aqueous solution 2 in Fable 1) to an aqueous solution shown in Table
1 which contained at least one kind of divalent cation (M
2+) and at least one kind of trivalent cation (M
3+) (Composition of aqueous solution in Table 1). In this process, the pH of the reaction
suspension liquid was adjusted to be 10±0.1 by dropping a 2.0 M NaOH solution. Next,
each of the obtained precipitates was filtered and dried to give a powdery layered
double hydroxide. The obtained powdery substances were identified as being layered
double hydroxides by X-ray diffractometry.
[0035] [Table 1]
Table 1
No |
Composition of aqueous solution 1 |
Composition of aqueous solution 2 |
Composition of crystalline layered substance (layered double hydroxide) (Identification
result) |
1 |
Magnesium nitrate hexahydrate 113g/L Aluminum nitrate nonahydrate 83g/L |
Sodium carbonate decahydrate 31g/L |
ICDD card reference code 01-089-0460 [Mg0.667Al0.333(OH)2][CO32-]0.167·0.5H2O Magnesium Aluminum Hydroxide Carbonate Hydrate |
2 |
Zinc nitrate heptahydrate 131g/L Aluminum nitrate nonahydrate 83g/L |
Sodium carbonate decahydrate 31g/L |
ICDD card reference code 00-048-1021 [Zn0.71Al0.29(OH)2][CO32-]0.145·H2O Zinc Aluminum Carbonate Hydroxide Hydrate |
3 |
Iron (II) sulfate heptahydrate 122g/L Iron (III) nitrate nonahydrate 89g/L |
Sodium carbonate decahydrate 31g/L |
ICDD card reference code 00-050-1380 [Fe0.67Fe0.33(OH)2][CO32]0.145 0.33H2O Iron Carbonate Hydroxide Hydrate |
4 |
Nickel nitrate hexahydrate 128g/L Iron (III) titrate nonahydrate 89g/L |
Sodium sulfate decahydrate 31g/L |
ICDD card reference code 00-042-0573 [Ni0.75Fe0.25(OH)2][SO42-]0.1250.5H2O Iron Nickel Sulfate Hydroxide Hydrate |
5 |
Magnesium nitrate hexahydrate 113g/L Aluminum nitrate nonahydrate 83g/L |
Sodium hydroxide 5g/L |
ICDD card reference code 00-038-0478 [Mg0.75Al0.25(OH)2][OH-]0.25·0·5H2O Magnesium Aluminum Hydroxide Hydrate |
6 |
Magnesium nitrate hexahydrate 113g/L Iron (III) nitrate 89g/L |
Sodium chloride 6g/L |
ICDD card reference code 00-020-0500 [Mg0.75Fe0.25(OH)2][Cl-]0.250.5H2O Magnesium Iron Oxide Chloride Hydroxide Hydrate |
7 |
Calcium nitrate tetrahydrate 104g/L Aluminum nitrate nonahydrate 83g/L |
Sodium chloride 6g/L |
ICDD card reference code 00-035-0105 [Ca0.67Al0.33(OH)2][Cl-]0.330.67H2O Calcium Aluminum Hydroxide Chloride Hydrate |
8 |
Magnesium titrate hexahydrate 113g/L Chromium (III) nitrate nonahydrate 88g/L |
Sodium carbonate decahydrate 31g/L |
ICDD card reference code 00-045-1475 [Mg0.67Cr0.33(OH)2][CO32-]0.157·0.5H2O Magnesium Chromium Carbonate Hydroxide Hydrate |
9 |
Iron (II) sulfate heptahydrate 122g/L Aluminum titrate nonahydrate 83g/L |
Sodium carbonate decahydrate 31g/L |
ICDD card reference code 00-051-1527 [Fe0.67Al0.33(OH)2][CO32-]0.157 0.5H2O Iron Aluminum Oxide Carbonate Hydroxide Hydrate |
10 |
Nickel nitrate hexahydrate 128g/L Aluminum nitrate nonahydrate 83g/L |
Sodium carbonate decahydrate 31g/L |
ICDD card reference code 00-015-0087 [Ni0.67Al0.33(OH)2][CO32-]0.157·0.5H2O Nickel Aluminum Oxide Carbonate Hydroxide Hydrate |
[0036] According to the formulations described in Table 3, the layered double hydroxides
prepared by the above process were appropriately mixed together with any of organic
resin compositions shown in Table 2, and each mixture was stirred using a coating
disperser (a sand grinder) for 45 minutes to give a coating composition for forming
an organic inorganic complex coating on the surface of a galvanized steel sheet.
[0037] [Table 2]
Table 2
No. |
Type |
Base resins |
1 |
Thermosetting resins |
Amine-modified epoxy resin/blocked isocyanate curing agent |
2 |
Urethane-modified epoxy resin/blocked isocyanate curing agent |
3 |
Epichlorohydrin epoxy resin/blocked isocyanate curing agent |
4 |
Polyester urethane resin/melamine curing agent |
5 |
Water-dispersible resins |
Ionomer of ethylene-acrylic acid copolymer |
6 |
Ethylene-acryl copolymer (emulsion polymerization) |
7 |
Styrene-acryl copolymer |
8 |
Polyurethane resin |
[0038] Cold rolled steel sheets having a sheet thickness of 0.7 mm were provided as base
steel sheets. A galvannealed coating was formed on each steel sheet by a common method,
and the coated steel sheet was temper rolled. Separately, a hot dip zinc coating or
an electrolytic zinc coating was formed on similar steel sheets by a common method.
The surface of each of the various coated steel sheets obtained as described above
was degreased with an alkali, washed with water and dried. Thereafter, any of the
coating compositions was applied to the surface of the steel sheet with a roll coater
and was baked (thermally dried) at a baking temperature shown in Table 3 (140°C).
The thickness of the organic inorganic complex coating was adjusted by controlling
the solid content (the content of residues after heating) of the coating composition
or application conditions (such as roll force or rotational speed).
[0039] The organic inorganic complex coatings formed on the surface of the galvannealed
steel sheets, the hot dip galvanized steel sheets and the electrolytically galvanized
steel sheets were analyzed in order to measure the average film thickness as well
as to identify the layered double hydroxides. To evaluate press-formability, sliding
properties were evaluated by measuring the friction coefficient and evaluating galling
properties. The methods used for the measurements and the identification are described
below.
1) Measurement of average film thickness of organic inorganic complex coating
[0040] The coating was sputtered at an angle of 45° using FIB and the cross section was
observed by ultralow-accelerating-voltage SEM. The values of film thickness measured
at 10 sites were averaged to determine the film thickness of the coating.
2) Identification of layered double hydroxide
[0041] The presence of crystalline layered double hydroxide was confirmed by X-ray diffractometry.
The peaks which were obtained by X-ray diffractometry using Cu-Kα radiation were verified
against ICDD cards and the layered double hydroxide was identified. The cards which
agreed with the obtained data are described below.
i) Magnesium Aluminum Hydroxide Carbonate Hydrate
ICDD card reference code: 01-089-0460
[Mg0.667Al0.333(OH)2][CO32-]0.167·0.5H2O
ii) Zinc Aluminum Carbonate Hydroxide Hydrate
ICDD card reference code: 00-048-1021
[Zn0.71Al0.29(OH)2][CO32-]0.145·H2O
iii) Iron Carbonate Hydroxide Hydrate
ICDD card reference code: 00-050-1380
[Fe0.67Fe0.33(OH)2][CO32-]0.145·0.33H2O
iv) Iron Nickel Sulfate Hydroxide Hydrate
ICDD card reference code: 00-042-0573
[Ni0.75Fe0.25(OH)2][SO42-]0.125·0.5H2O
v) Magnesium Aluminum Hydroxide Hydrate
ICDD card reference code: 00-038-0478
[Mg0.75Al0.25(OH)2][OH-]0.25·0.5H2O
vi) Magnesium Iron Oxide Chloride Hydroxide Hydrate
ICDD card reference code: 00-020-0500
[Mg0.75Fe0.25(OH)2][Cl-]0.25·0.5H2O
vii) Calcium Aluminum Hydroxide Chloride Hydrate
ICDD card reference code: 00-035-0105
[Ca0.67Al0.33(OH)2][Cl-]0.33·0.67H2O
viii) Magnesium Chromium Carbonate Hydroxide Hydrate
ICDD card reference code: 00-045-1475
IM90.67Cr0.33(OH)2][CO32-]0.157·0.5H2O
ix) Iron Aluminum Oxide Carbonate Hydroxide Hydrate
ICDD card reference code: 00-051-1527
[Fe0.67Al0.33(OH)2][CO32-]0.157·0.5H2O
x) Nickel Aluminum Oxide Carbonate Hydroxide Hydrate
ICDD card reference code: 00-015-0087
[Ni 0.67Al0.33(OH)2][CO32-,OH-]0.157·0.5H2O
3) Measurement of friction coefficient
[0042] In order to evaluate press-formability (in particular, formability at a portion of
steel sheet which was in contact with an object when the steel sheet would be drawn
or slid), the dynamic friction coefficient of each test material was measured in the
following manner. Fig. 1 is a schematic front view illustrating a friction coefficient
measuring apparatus. As illustrated in the figure, a friction coefficient measurement
sample 1 collected from the test material was fixed on a sample table 2. The sample
table 2 was fixed on the upper surface of a horizontally movable slide table 3. Under
the lower surface of the slide table 3, a vertically movable slide table support 5
was provided which had rollers 4 in contact with the lower surface of the slide table
3. The slide table support 5 was fitted with a first load cell 7 which was capable
of measuring pressure load N applied by a bead 6 to the friction coefficient measurement
sample 1 as a result of the elevation of the slide table support. At one end of the
slide table 3, a second load cell was provided which was capable of measuring sliding
frictional force F caused when the slide table 3 was moved in the horizontal direction
while applying the pressure force. Prior to the testing, the surface of the friction
coefficient measurement sample 1 was coated with a lubricant oil which was press washing
oil PRETON R352z manufactured by Sugimura Chemical Industrial Co., Ltd.
[0043] Fig. 2 is a schematic perspective view illustrating the shape and the size of one
of the used beads (hereinafter, bead shape 1). The friction coefficient measurement
sample 1 was caused to slide while the lower surface of the bead 6 was pressed against
the surface of the sample. The bead 6 shown in Fig. 2 was 10 mm in width and 12 mm
in length in the sample sliding direction. The lower edges of the bead in the sliding
direction each had a curved surface with a curvature of 4.5 mmR. The lower surface
of the bead against which the sample was to be pressed was a flat surface 10 mm in
width and 3 mm in length in the sliding direction.
[0044] Fig. 3 is a schematic perspective view illustrating the shape and the size of one
of the used beads (hereinafter, bead shape 2). The friction coefficient measurement
sample 1 was caused to slide while the lower surface of the bead 6 was pressed against
the surface of the sample. The bead 6 shown in Fig. 3 was 10 mm in width and 69 mm
in length in the sample sliding direction. The lower edges of the bead in the sliding
direction each had a curved surface with a curvature of 4.5 mmR. The lower surface
of the bead against which the sample was to be pressed was a flat surface 10 mm in
width and 60 mm in length in the sliding direction.
[0045] The measurement of friction coefficient was carried out under any of 3 conditions
in which the temperature was room temperature (25°C) and the pressure load N was 400,
1200 or 1600 kgf so that the contact pressure would be a value expected in the press
forming of high-strength steel sheets. Further, the pulling rate (the velocity of
horizontal movement of the slide table 3) for the sample was 100 cm/min or 20 cm/min.
The pressure load N and the sliding frictional force F were measured under any of
these conditions. The friction coefficient µ between the test material and the bead
was calculated from the equation: µ = F/N. The bead shape, the pressure load conditions
and the pulling rate were used in the following combinations.
Condition 1: bead shape 1, pressure load 400 kgf and pulling rate 100 cm/min
Condition 2: bead shape 1, pressure load 1200 kgf and pulling rate 100 cm/min
Condition 3: bead shape 1, pressure load 1600 kgf and pulling rate 100 cm/min
Condition 4: bead shape 2, pressure load 400 kgf and pulling rate 20 cm/min
4) Evaluation of galling properties
[0046] Galvanized steel sheets coated with pure zinc increase the sliding friction due to
the coating having become attached to a mold after the coated portion has undergone
a long sliding distance. Thus, galling tendency is an important property in addition
to the dynamic friction coefficient. Using the friction coefficient measuring apparatus
illustrated in Fig. 1, a sliding test was repeatedly carried out 50 times. The number
of repetition which caused an increase in friction coefficient of 0.01 or more was
determined. Galling properties were evaluated assuming that galling would be caused
at the obtained number of repetition. When there was no increase in friction coefficient
even after the sliding test was repeated 50 times, the number of repetition was determined
to be at least 50 times. Similarly to 3) Measurement of friction coefficient, the
test was carried out under any of the above-described conditions 1 to 3 so that the
contact pressure would be a value expected in the press forming of high-strength steel
sheets.
The results obtained by these tests as well as the test conditions are described in
Table 3.
[0047] [Table 3]
Table 3
Category |
No. |
Coated steel sheet type |
Surface coating layer |
Friction coefficient |
Mold scoring properties |
Organic resin |
Crystalline layered substance |
Average film thickness (µm) |
Baking Temp (°C) |
Cond 1 |
Cond 2 |
Cond 3 |
Cond 4 |
Cond 1 |
Cond 2 |
Cond 3 |
Kind *2 |
Amount *3 |
Kind *1 |
Amount *3 |
CompEx |
1 |
|
1 |
100 |
- |
- |
10 |
140 |
0 127 |
0 049 |
0047 |
0280 |
5 |
3 |
2 |
Inv Ex. |
2 |
|
1 |
100 |
1 |
20 |
10 |
140 |
0 062 |
0025 |
0017 |
0 142 |
at least 54 |
32 |
22 |
Inv Ex. |
3 |
|
1 |
100 |
2 |
20 |
10 |
140 |
0 060 |
0 024 |
0 017 |
0 142 |
at least 50 |
33 |
23 |
Inv Ex. |
4 |
|
1 |
100 |
3 |
20 |
10 |
140 |
0061 |
0026 |
0016 |
0143 |
at least 50 |
30 |
20 |
Inv Ex. |
5 |
|
1 |
100 |
4 |
20 |
10 |
140 |
0 059 |
0024 |
0016 |
0142 |
at least 50 |
31 |
21 |
Inv Ex. |
6 |
|
1 |
100 |
5 |
20 |
10 |
140 |
0058 |
0024 |
0016 |
0143 |
at least 50 |
33 |
20 |
Inv Ex. |
7 |
|
1 |
100 |
6 |
20 |
10 |
140 |
0060 |
0024 |
0017 |
0140 |
at least 50 |
35 |
20 |
Inv Ex. |
8 |
|
1 |
100 |
7 |
20 |
10 |
140 |
0061 |
0025 |
0017 |
0142 |
at least 50 |
29 |
23 |
Inv Ex. |
9 |
|
1 |
100 |
8 |
20 |
10 |
140 |
0059 |
0025 |
0018 |
0142 |
at least 50 |
28 |
23 |
Inv Ex. |
10 |
|
1 |
100 |
9 |
20 |
10 |
140 |
0060 |
0025 |
0018 |
0143 |
at least 50 |
31 |
25 |
Inv Ex. |
11 |
|
1 |
100 |
10 |
20 |
10 |
140 |
0 060 |
0 026 |
0017 |
0140 |
at least 50 |
30 |
22 |
Inv Ex. |
12 |
|
2 |
100 |
1 |
20 |
10 |
140 |
0 060 |
0025 |
0 017 |
0141 |
at least 50 |
32 |
22 |
Inv Ex |
13 |
Hot dip galvanized steel sheet (G1) |
3 |
100 |
1 |
20 |
10 |
140 |
0062 |
0 024 |
0016 |
0 141 |
at least 50 |
33 |
22 |
Inv Ex. |
14 |
|
4 |
100 |
1 |
20 |
10 |
140 |
0061 |
0025 |
0017 |
0140 |
at least 50 |
35 |
23 |
Inv Ex. |
15 |
|
5 |
100 |
1 |
20 |
10 |
140 |
0059 |
0025 |
0018 |
0140 |
at least 50 |
33 |
26 |
Inv Ex. |
16 |
|
6 |
100 |
1 |
20 |
10 |
140 |
0 060 |
0025 |
0016 |
0140 |
at least 50 |
32 |
25 |
Inv Ex. |
17 |
|
7 |
100 |
1 |
20 |
10 |
140 |
0061 |
0025 |
0016 |
0140 |
at least 50 |
29 |
22 |
Inv Ex. |
18 |
|
8 |
100 |
1 |
20 |
10 |
140 |
0 060 |
0026 |
0016 |
0142 |
at least 50 |
28 |
24 |
Inv Ex. |
19 |
|
1 |
100 |
1 |
05 |
10 |
140 |
0071 |
0030 |
0025 |
0162 |
39 |
20 |
10 |
Inv Ex. |
20 |
|
1 |
100 |
1 |
1 |
10 |
140 |
0068 |
0029 |
0022 |
0155 |
41 |
21 |
12 |
Inv Ex. |
21 |
|
1 |
100 |
1 |
10 |
10 |
140 |
0065 |
0027 |
0020 |
0150 |
45 |
25 |
16 |
Inv Ex. |
22 |
|
1 |
100 |
1 |
100 |
10 |
140 |
0055 |
0020 |
0013 |
0134 |
at least 50 |
at least 50 |
at least 50 |
Inv Ex. |
23 |
|
1 |
100 |
1 |
120 |
10 |
140 |
0050 |
0019 |
0012 |
0129 |
at least 50 |
at least 50 |
at least 50 |
Inv Ex. |
24 |
|
1 |
100 |
1 |
20 |
01 |
140 |
0072 |
0030 |
0025 |
0162 |
39 |
20 |
10 |
Inv Ex. |
25 |
|
1 |
100 |
1 |
20 |
05 |
140 |
0068 |
0 028 |
0022 |
0155 |
41 |
21 |
12 |
Inv Ex. |
26 |
|
1 |
100 |
1 |
20 |
15 |
140 |
0056 |
0020 |
0013 |
0134 |
at least 50 |
at least 50 |
42 |
Inv Ex. |
27 |
|
1 |
100 |
1 |
20 |
20 |
140 |
0052 |
0019 |
0012 |
0129 |
at least 50 |
at least 50 |
at least 50 |
Comp Ex |
28 |
|
1 |
100 |
|
|
10 |
140 |
0176 |
0118 |
0111 |
0213 |
- |
- |
- |
Inv Ex. |
29 |
|
1 |
100 |
1 |
20 |
10 |
140 |
0064 |
0026 |
0019 |
0142 |
- |
- |
- |
Inv Ex. |
30 |
|
1 |
100 |
2 |
20 |
10 |
140 |
0062 |
0 025 |
0019 |
0143 |
- |
- |
- |
Inv Ex. |
31 |
|
1 |
100 |
3 |
20 |
10 |
140 |
0061 |
0025 |
0018 |
0143 |
- |
- |
- |
Inv Ex. |
32 |
|
1 |
100 |
4 |
20 |
10 |
140 |
0060 |
0025 |
0017 |
0143 |
- |
- |
- |
Inv Ex |
33 |
Galvannealed steel sheet (GA) |
1 |
100 |
5 |
20 |
10 |
140 |
0060 |
0026 |
0019 |
0143 |
- |
- |
- |
Inv Ex |
34 |
|
1 |
100 |
6 |
20 |
10 |
140 |
0062 |
0026 |
0017 |
0142 |
- |
- |
- |
Inv Ex. |
35 |
|
1 |
100 |
7 |
20 |
10 |
140 |
0063 |
0026 |
0017 |
0140 |
- |
- |
- |
Inv Ex. |
36 |
|
1 |
100 |
8 |
20 |
10 |
140 |
0062 |
0024 |
0016 |
0140 |
- |
- |
- |
Inv Ex |
37 |
|
1 |
100 |
9 |
20 |
10 |
140 |
0060 |
0024 |
0017 |
0143 |
- |
- |
- |
Inv Ex. |
38 |
|
1 |
100 |
10 |
20 |
10 |
140 |
0062 |
0024 |
0017 |
0143 |
- |
- |
- |
Comp Ex |
39 |
|
1 |
100 |
- |
- |
10 |
140 |
0112 |
0042 |
0041 |
0.248 |
3 |
2 |
1 |
Inv Ex. |
40 |
|
1 |
100 |
1 |
20 |
10 |
140 |
0062 |
0025 |
0018 |
0143 |
at least 50 |
32 |
22 |
Inv Ex. |
41 |
|
1 |
100 |
2 |
20 |
10 |
140 |
0060 |
0024 |
0018 |
0143 |
at least 50 |
33 |
23 |
Inv Ex |
42 |
|
1 |
100 |
3 |
20 |
10 |
140 |
0063 |
0024 |
0018 |
0142 |
at least 50 |
30 |
20 |
Inv Ex. |
43 |
|
1 |
100 |
4 |
20 |
10 |
140 |
0062 |
0026 |
0019 |
0140 |
at least 50 |
31 |
21 |
Inv Ex. |
44 |
Electrolytically galvanized steel sheet (EG) |
1 |
100 |
5 |
20 |
10 |
140 |
0061 |
0025 |
0017 |
0142 |
at least 50 |
33 |
20 |
Inv E. |
45 |
|
1 |
100 |
6 |
20 |
10 |
140 |
0062 |
0025 |
0017 |
0141 |
at least 50 |
35 |
20 |
Inv Ex. |
46 |
|
1 |
100 |
7 |
20 |
10 |
140 |
0062 |
0024 |
0017 |
0142 |
at least 50 |
29 |
23 |
Inv Ex. |
47 |
|
1 |
100 |
8 |
20 |
10 |
140 |
0063 |
0024 |
0018 |
0143 |
at least 50 |
28 |
23 |
Inv Ex. |
48 |
|
1 |
100 |
9 |
20 |
10 |
140 |
0061 |
0024 |
0019 |
0141 |
at least 50 |
31 |
25 |
Inv Ex |
49 |
|
1 |
100 |
10 |
20 |
10 |
140 |
0061 |
0024 |
0018 |
0141 |
at least 50 |
30 |
22 |
*1 No of crystalline layered substance described in Table 1
*2 No of organic resin described in Table2 2
*3 parts by weight (solid content) wt% |
[0048] The test results described in Table 3 show the following.
Sample No. 1 using a hot dip galvanized steel sheet (GI) was a comparative example
without any crystalline layered substance being contained. The friction coefficient
was high and the galling properties were poor. Samples Nos. 2 to 27 were inventive
examples containing the organic resin and the crystalline layered substance. In comparison
with the results of Comparative Example No. 1, the friction coefficient was low and
the galling properties were good.
[0049] Sample No. 28 using a galvannealed steel sheet (GA) was a comparative example without
any crystalline layered substance being contained. The friction coefficient was high.
Samples Nos. 29 to 38 were inventive examples containing the organic resin and the
crystalline layered substance. In comparison with the results of Comparative Example
No. 28, the friction coefficient was low.
[0050] Sample No. 39 using an electrolytically galvanized steel sheet (EG) was a comparative
example without any crystalline layered substance being contained. The friction coefficient
was high and the galling properties were poor. Samples Nos. 40 to 49 were inventive
examples containing the organic resin and the crystalline layered substance. In comparison
with the results of Comparative Example No. 39, the friction coefficient was low and
the galling properties were good.
Industrial Applicability
[0051] The galvanized steel sheets according to the present invention are excellent in press-formability
and can be used in various fields, in particular for automobile bodies which are necessarily
manufactured from hardly formable materials.
Reference Signs List
[0052]
- 1
- FRICTION COEFFICIENT MEASUREMENT SAMPLE
- 2
- SAMPLE TABLE
- 3
- SLIDE TABLE
- 4
- ROLLERS
- 5
- SLIDE TABLE SUPPORT
- 6
- BEAD
- 7
- FIRST LOAD CELL
- 8
- SECOND LOAD CELL
- 9
- RAIL
- N
- PRESSURE LOAD
- F
- SLIDING FRICTIONAL FORCE
1. A galvanized steel sheet which has an organic inorganic complex coating containing
an organic resin and a crystalline layered substance on the surface, the organic inorganic
complex coating having an average film thickness of 0.10 to 2.0 µm and containing
the crystalline layered substance in a solid content of not less than 0.5 parts by
weight with respect to 100 parts by weight of the solid content of the organic resin.
2. The galvanized steel sheet according to Claim 1, wherein the crystalline layered substance
is a layered double hydroxide represented by [M2+1-xM3+x(OH)2][An-]x/n·zH2O wherein M2+ is one, or two or more selected from Mg2+, Ca2+, Fe2+, Ni2+, Zn2+, Pb2+ and Sn2+, M3+ is one, or two or more selected from Al3+, Fe3+, Cr3+ , 3/4Zr4+ and Mo3+, and An- is one, or two or more selected from OH-, F-, CO32-, Cl-, Br-, (C2O4)2-, I-, (NO3)-, (SO4)2-, (BrO3)-, (IO3)-, (V10O28)6-, (Si2O5)2-, (ClO4)-, (CH3COO)-, [C6H4(CO2)2]2-, (C6H5COO)-, [C8H16(CO2)2]2-, n(C8H17SO4)-, n (C12H25SO4)-, n(C18H37SO4)- and SiO44-.
3. The galvanized steel sheet according to Claim 1, wherein the crystalline layered substance
is a layered double hydroxide represented by [M2+1-xM3+x(OH)2] [An-]x/n· zH2O wherein M2+ is one, or two or more selected from Mg2+, Ca2+, Fe2+, Ni2+ and Zn2+, M3+ is one, or two or more selected from Al3+, Fe3+ and Cr3+, and An- is one, or two or more selected from OH-, CO32-, Cl- and (SO4)2-.
4. The galvanized steel sheet according to any one of Claims 1 to 3, wherein the organic
resin is one, or two or more selected from epoxy resins, modified epoxy resins, polyhydroxy
polyether resins, polyalkylene glycol-modified epoxy resins, urethane-modified epoxy
resins, resins obtained by further modifying these resins, polyester resins, urethane
resins, silicon resins and acrylic resins.